Beam shaping apparatus

Abstract

Disclosed herein is a radiation head for a radiotherapy device. The radiation head comprises a source of radiation configured to emit a beam of radiation; and beam shaping device for collimating the beam of radiation. The beam shaping device comprises a multi-leaf collimator; and a diaphragm positioned between the source and the multi-leaf collimator. The diaphragm comprises a diaphragm block movable along a curved path, the diaphragm block having a flat face focused on a focus point which is offset from the source of radiation.

The invention claimed is: 
     
         1 . A radiation head for a radiotherapy device, the radiation head comprising:
 a source of radiation configured to emit a beam of radiation;   a beam shaping device for collimating the beam of radiation, the beam shaping device comprising:   a multi-leaf collimator; and   a diaphragm positioned between the source of radiation and the multi-leaf collimator, the diaphragm comprising a diaphragm block having a flat face, the diaphragm block moveable along a curved path with the flat face focused on a focus point which is above the source of radiation such that a lower portion of the diaphragm block extends into the beam by a greater amount than an upper portion of the diaphragm block.   
     
     
         2 . The radiation head according to  claim 1 , wherein the diaphragm is located below the source of radiation. 
     
     
         3 . The radiation head according to  claim 1 , wherein the focus point is offset from the source of radiation by a distance d. 
     
     
         4 . The radiation head according to  claim 1 , wherein the source of radiation is configured to emit the beam of radiation directed along a beam axis and having a width transverse to the beam axis in a first direction and a second direction, wherein the diaphragm block selectively limits the width of the beam in the first direction. 
     
     
         5 . The radiation head according to  claim 1 , wherein the beam shaping device defines an aperture to delimit the beam, and wherein the diaphragm block spans an edge of the aperture. 
     
     
         6 . The radiation head according to  claim 1 , wherein the diaphragm block is slidably attached to a curved rail which defines the curved path. 
     
     
         7 . The radiation head according to  claim 1 , wherein the diaphragm comprises a first diaphragm block and a second diaphragm block defining opposing edges of an aperture to delimit the beam. 
     
     
         8 . The radiation head according to  claim 4 , wherein the multi-leaf collimator is configured to selectively limit the width of the beam in the second direction. 
     
     
         9 . The radiation head according to  claim 7 , wherein the first diaphragm block and the second diaphragm block are movable along the curved path and focused on the focus point. 
     
     
         10 . The radiation head according to  claim 7 , wherein the source of radiation comprises:
 a nominal disc, wherein at a maximum field angle the first diaphragm block is focused on a first edge of the nominal disc and the second diaphragm block is focused on a second edge of the nominal disc.   
     
     
         11 . A radiotherapy apparatus comprising:
 a rotatable gantry;   a radiation head fixedly attached to the rotatable gantry, the radiation head comprising:   a source of radiation configured to emit a beam of radiation;   a beam shaping device for collimating the beam of radiation, the beam shaping device comprising:   a multi-leaf collimator; and   a diaphragm positioned between the source of radiation and the multi-leaf collimator, the diaphragm comprising a diaphragm block having a flat face, the diaphragm block movable along a curved path with the flat face focused on a focus point which is above the source of radiation such that a lower portion of the diaphragm block extends into the beam by a greater amount than an upper portion of the diaphragm block.   
     
     
         12 . The radiotherapy apparatus of  claim 11 , wherein the diaphragm is located below the source of radiation. 
     
     
         13 . The radiotherapy apparatus of  claim 11 , wherein the focus point is offset from the source of radiation. 
     
     
         14 . The radiotherapy apparatus of  claim 11 , wherein the beam shaping device defines an aperture to delimit the beam, and wherein the diaphragm block spans an edge of the aperture. 
     
     
         15 . The radiotherapy apparatus of  claim 11 , wherein the diaphragm block is slidably attached to a curved rail which defines the curved path. 
     
     
         16 . The radiotherapy apparatus of  claim 11 , wherein the diaphragm comprises a first diaphragm block and a second diaphragm block defining opposing edges of an aperture to delimit the beam. 
     
     
         17 . A radiotherapy apparatus comprising:
 a rotatable gantry; and   a radiation head fixedly attached to the rotatable gantry, the radiation head comprising:   a source of radiation configured to emit a beam of radiation; and   a beam shaping device for collimating the beam of radiation that is directed along a beam axis and has a width transverse to the beam axis in a first direction and a second direction, the beam shaping device comprising:   a multi-leaf collimator;   a diaphragm positioned between the source of radiation and the multi-leaf collimator, the diaphragm comprising a diaphragm block movable along a curved path, the diaphragm block having a flat face focused on a focus point which is offset from the source of radiation; and   a drive member, the drive member comprising:   a gear fixedly attached to the diaphragm block;   a worm screw; and   a motor configured to drive the worm screw, wherein the gear is engaged with the worm screw such that rotation of the worm screw causes motion of the diaphragm block in the second direction.   
     
     
         18 . The radiotherapy apparatus of  claim 17 , wherein the diaphragm block is movably attached to a chassis, and wherein the motor is attached to the chassis via a mount. 
     
     
         19 . The radiotherapy apparatus of  claim 17 , wherein the curved path is a curved rail, wherein the diaphragm block is slidably attached to the curved rail by a slide, and wherein the slide is fixedly attached to the diaphragm block. 
     
     
         20 . The radiotherapy apparatus of  claim 18 , wherein the diaphragm block is movable along a curved rail which is attached to the chassis.